"This statement does not mean the halt of military action," the defence minister's press secretary, Artsrun Hovhannisyan, said on Facebook.

Nagorno-Karabakh has been under the control of local ethnic Armenian forces and the Armenian military since a war ended in 1994.

The Armenia Defence Ministry said Azerbaijani troops started an offensive with tanks and artillery on Saturday. Azerbaijan denied those allegations, saying its soldiers were reacting to heavy attacks from the Armenian side.

Armenia said 18 of its forces were killed and Azerbaijan reported it had 12 dead.

Analysts say the conflict is fuelled by long-simmering tensions in the region between Christian Armenians and mostly Muslim Azeris.

Al Jazeera's Rory Challands, reporting from Moscow, said the dispute between the two nations had the potential to spiral into a serious regional conflict.

"The trigger for the surge in fighting still seems to be local but the reasons still appear to be quite murky," he said.